The present invention relates to a method of manufacturing a cylindrical mechanical filter basket for centripetal or centrifugal flow, the basket comprising metal rings spaced along an axis of the basket and wires that are regularly spaced apart relative to one another and disposed around the periphery of the rings so as to form a cylindrical sieve.
Such a basket is generally used to filter an initial material by passing it through the sieve formed by the regularly spaced-apart wires so as to split the initial material into a first material of thick consistency that has not been able to pass through the sieve, and second material of more fluid consistency that has passed through the sieve. Thus, the initial material situated inside the basket can be caused to pass through the sieve, for example, by a centrifugal effect by causing the basket to rotate about its axis with rotary motion that is continuous or oscillatory, or that can be driven by a rotor placed inside the basket, so that at the end of the operation the first material can be recovered from the inside of the basket and the second material from the outside of the basket.
By way of example, such a basket is commonly used in the papermaking industry to filter paper pulp, however use thereof is more general and can be applied to other types of material that are to be filtered.
In the prior art concerning the manufacture of such baskets, it is the general practice in a first operation to make a plane sieve which is constituted by bars that are positioned horizontally and which have vertically-positioned wires attached thereto, e.g. by electric resistance welding or by binding, and then in a second operation the sieve is curved and the ends of the bars are welded together so as to form a cylindrical sieve.
The drawbacks of that solution lie not only in the rolling-up operation which generates firstly internal stresses in the basket tending to reduce its lifetime and which secondly represents extra manufacturing cost, but also in problems to do with the lifetime of the welds.
Thus, the lifetime of present baskets is relatively short, for a manufacturing cost that is relatively high.
The object of the invention is to remedy those drawbacks.
To this end, the invention provides a method of manufacturing a cylindrical mechanical filter basket for centripetal or centrifugal flow, the basket comprising metal rings spaced apart along an axis of the basket and wires regularly spaced apart from one another and disposed around the periphery of the rings to form a cylindrical sieve, the method being characterized in that it consists in:
a) providing shaped rings each having an annular core, an annular rim of smaller thickness than the annular core, at least one annular shoulder between the annular rim and the annular core, and notches regularly spaced apart in the rim;
b) placing wires in the notches of the rings so that the wires are disposed regularly spaced apart from one another around the periphery of the rings; and
c) moving a heat source along the shoulder of each ring, the source being at a temperature that is high enough to melt the shoulder so that the molten metal from the shoulder provides a weld between each wire and the ring without any external filler metal.
With such a method of manufacture, the quality of the welds between the wires and the rings is improved, so the basket has greater strength, which increases its lifetime, while its manufacturing cost is less than the cost of manufacturing a conventional basket.
In particular implementations of the method of the invention, a ring is supplied with a rim that is thin enough to facilitate the machining of notches for receiving the wires, and a core that is thick enough to withstand the radial forces generated by the filtering operation, for example. Furthermore, it is also possible to provide wires of a particular section, e.g. comprising a root-forming portion of shape complementary to the notches so as to prevent the wire from turning relative to the ring while it is being put into position and further improve the quality of the welding between the rings and the wires so as to further increase the lifetime of the basket.
Finally, making a first weld on the top face of each ring and a second weld on the bottom face of each ring further increases the strength of the connections between the wires and the rings.